To the Editor: In their study of the relationship between time of day, timeliness of reperfusion, and in-hospital mortality for patients with acute ST-segment elevation myocardial infarction, Dr Magid and colleagues1 used data from the United States National Registry of Myocardial Infarction and found that patients presenting during off-hours had higher in-hospital mortality than those presenting during regular hours. Moreover, percutaneous coronary intervention reperfusion times were greater during off-hours than regular hours; this might contribute to higher off-hours in-hospital mortality.